Device for the displacement of magnetic read/write heads

ABSTRACT

A device is provided for the displacement of magnetic read and write heads in a disc drive unit, which device includes a sliding carriage on which the heads are mounted. The carriage is driven by an electric motor comprising a coil integral with the carriage and located in the magnetic field of a permanent magnet consisting of a magnetic core around which the coil is coaxially located. An air dash-pot is provided having one of its constituent elements attached to the carriage and the other to the core.

United States Patent 1191 1111 3,827,081 Prieur July 30, 1974 1 DEVICE FOR THE DISPLACEMENT 0F 2.481.398 9/1949 Danisch 179/1002 c MAGNETIC READ/WRITE HEADS FOREIGN PATENTS OR APPLICATIONS [75] memo Lucie" Prim", Ecouen, 1 056 888 2/1967 Great Britain 310/14 France [73] Assignee: Societe Industrielle Honeywell Bull primary E 1 i R p i (Societe Anonyme), Paris, France Filed: June 20, 1972 Appl. No.: 264,640

Foreign Application Priority Data June 24,1971 France 71.23131 US. Cl. 360/105, 310/13 lnt.Cl. Gllb 5/54,Gl1b 21/24 Field of Search 274/4 A; 310/14, 23, 15,

3l0/16,17,12,13;179/100.2 C, 100.2 CA

References Cited UNITED STATES PATENTS 12/1947 Miller 310/17 Assistant ExaminerA. Jason Mirabito Attorney, Agent, or Firm-Fred Jacob 5 7 ABSTRACT comprising a coil integral with the carriage and located in the magnetic field of a permanent magnet consisting of a magnetic core around which the coil is coaxially located. An air dash-pot is provided having one of its constituent elements attached to the carriage and the other to the core.

13 Claims, 3 Drawing Figures DEVICE FOR THE DISPLACEMENT OF MAGNETIC READ/WRITE HEADS BACKGROUND OF THE INVENTION The present invention deals with a clamping device for the displacement of magnetic heads, a device which is especially designed for disk memory units to guide such heads onto the desired recording track of the disks or to remove the head from the recording track.

Devices of the subject type are now known in which the magnetic heads are carried by a sliding carriage driven by an electric motor of the type termed voicecoil, which includes a mobile electric coil positioned in a magnetic field and fed by a current of variable intensity and polarity. Usually, this magnetic field is generated by a permanent magnet which is provided with a cylindric shell sheathing a cylindric magnetic core over which the coil is arranged coaxially. Such a motor is known to subject the carriage which carries the magnetic heads to very sizable accelerations which may attain g. When due to the breakage of a coil wire during operation of the device it becomes impossible to brake the carriage electrically, the result will be that the latter will strike either the magnetic support or the permanent magnet with great intensity, according to the particular direction of the displacement.

To avoid the risk of the carriage striking the magnetic support it has been suggested that an elastic stop, generally of two different hardnesses be placed on its track. However, this stop has the disadvantage of pushing the carriage back with great intensity in the direction of the permanent magnet, which causes damage to the carriage and motor.

The present invention removes this disadvantage of the prior art.

SUMMARY OF THE INVENTION According to the invention, the damping device for the displacement of magnetic heads includes a sliding carriage carrying the magnetic heads which is driven by an electric motor consisting of a coil which is integral with said carriage and placed in a magnetic field of a permanent magnet that includes a cylindric magnetic core over which said coil is placed coaxially, and is distinguished in that it includes an air dash-pot whose one component is solidly attached to the carriage and the other to said core of the permanent magnet. Thus, the carriage cannot strike the permanent magnet.

So as to avoid too great a space requirement, the two component parts of the dash-pots one dimension, parallel to the direction of the displacement of the carriage, is relatively short in relation to the course of the latter and no interacting of the one with the other occurs, except when the carriage happens to be in the vicinity of the core. Preferably, either component of the dash-pot is equipped with at least one cylindric protrusion in fixed connection with a base plate, cooperating with a cylindric protrusion of the other to form at least one couple comprising a cylinder and a piston. Obviously, the component parts may include several other cylindric protrusions integral with said base plates and coaxial with the former, these other protrusions of the one fitting into those of the other. Thus, circulation baffle-plates are obtained for the air enclosed in the dash-pot.

It is recommended that the two parts of the dash-pot be arranged coaxially with the magnetic core and with the carriage. In this way it is possible to use this dashpot for centering purposes in the mounting of the carriage and the coil relative to the core.

Furthermore, in the case where the device includes a pick-up for determining the velocity of the carriage which pick-up is placed in a cylinder bore coaxial with said core, the two component parts of the dash-pot are equipped with central tubular protrusions making it possible to pass the movable part of the pick-up therethrough and forming a piston-cylinder couple. In this instance, one may best make use of the dash-pot for centering the pick-up so as to avoid the machining of this cylinder bore with the high degree of precision necessary. For this reason, the component part integral with the core in this case has in a cylindric protrusion whose interior diameter corresponds with that of the cylinder bore, this part resting with the flat surface of its base plate on the flat surface of the core end. Preferably this part is centered in relation to the core by fitting it with a sleeve which it carries on the flat face in a cylinder bore of short length, coaxial with the cylinde'r bore of the pick-up and of a greater diameter than the latter.

In an alternate version of the embodiment the part of the dash-pot attached to the carriage includes at least one magnetic section which is attracted to the core by the magnetic field. Thus, when the carriage is close to the magnetic core the magnetic field of the latter acts on the magnetic section by generating a retention force in this position. A force greater than this force must then be generated to remove the carriage from the magnet. The carriage, therefore, cannot accidentally move by itself in the direction of the magnetic support.

BRIEF DESCRIPTION OF THE DRAWING The figures of the attached drawing will facilitate an understanding of the embodiment of the invention, wherein:

FIG. 1 is a schematic illustration of the device to which the invention is applied;

FIGS. 2 and 3 are enlarged fragmentary longitudinal sectional views taken through two embodiments of the dash-pot, according to the invention. Identical reference numerals denote the same elements in these figures.

DESCRIPTION OF THE PREFERRED EMBODIMENT The damping device for the displacement of magnetic heads, shown in FIG. 1, includes a carriage 1 capable of sliding on the rails 2 and 3 in the direction of the arrows F and F The carriage I carries magnetic heads (not shown) and is driven by a motor 4 of the voice-coil type. The motor 4 includes a cylindric coil 5 integral with the carriage l and a permanent magnet equipped with a cylindric shell 6 in the shape of a partially enclosed hollow cylinder in whose interior a cylindric magnetic core 7 is positioned. The cylindric coil 5 is coaxial with the core 7, an air-gap 8 of the magnet being formed between the rim of the shell 6 and the free end of the core 7.

The movement of the coil 5, hence of the carriage I, is controlled by the current of variable amplitude and polarity passing through said coil. When the carriage 1 moves in the direction of the arrow F it approaches magnetic data storage (not shown) and in the direction of the arrow F it withdraws from it.

When after having been propelled in the direction of the arrow F a break occurs in a wire of the coil 5, the carriage 1 can no longer be arrested electrically and it continues to move in the direction of the magnetic storage. So as to prevent damage to the carriage, the magnetic heads and the magnetic data storage an elastic stop 9 is provided which is capable of interacting with a part 10 of the carriage. However, this stop pushes the carriage back with great intensity in the direction of the arrow F which may bring about damage to the motor 4 by the carriage 1. Such damage could also occur when the braking of said carriage during its normal return movement in the direction of the arrow F becomes electrically impossible. To remedy these inadequacies, in accordance with the invention a dash-pot is inserted between the free end of the core 7 and the wall in front of the carriage 1.

In the embodiment shown in FIG. 2 this dash-pot comprises two component parts 11 and 12 which interact and which are fixedly mounted on the core 7 and the carriage 1, respectively by any suitable means. The part 11 includes a flat base plate 13 by which it is firmly attached to the flat surface of the end 14 of the core 7 and two tubular protrusions 15 and 16. The part 12 comprises in the same manner a flat base plate 17 by which it is fixed to a flat surface 28 of the carriage 1 opposing the core 7, and two tubular protrusions 18 and 19. The one dimension of the protrusions 15, 16, 18, and 19, parallel to the direction F and F is relatively short, so that in the rest position of the heads (extreme position of the carriage in the direction F the situation is avoided where the carriage 1 lies remote from the core 7, which would result in an excessive space requirement. Thus, when the carriage 1 is relatively distant from the core 7 the parts 11 and 12 do not interact (position shown in FIG. 2). However, on the contrary, when the carriage is sufficiently close to the core 7 the protrusions 16 and 18 act as cylinders for the protrusions 15 and 19, respectively which serve as pistons. The air enclosed and compressed in the ringlike cavity, defined by the pair of cylinders and pistons, prevents the carriage 1 from striking the motor 4, and brakesit gently. In the course of its compression the air escapes partly between the protrusions l5, l8, and partly between the protrusions 16, 19. Thereafter, the damping quality of the carriage 1 depends on relative play between these protrusions.

The tubular protrusions 16 and 19 permit the passing of the movable magnetic shaft 20 of a carriage velocity pick-up. This pick-up, of a known type, comprises a coil 21 which is located in the central longitudinal cylinder bore 22 of the core 7 which surrounds the shaft 20, attached to one of the ends of the carriage 1. Thus, when the carriage moves it carries along the shaft 20 which generates a voltage in the coil 21 which amplitude depends on the speed of the carriage 1. The coil 21 is insulated from the core 7 by a sheathing tube 23.

It may further be seen that the dash-pot 11-12 makes possible the centering of the coil 5 and the carriage 1 relative to the core 7.

In the device of FIG. 3, the protrusion 16 of the part 11 has an inner diameter equal to that of the cylinder bore 22. In this fashion this part 11 may function,

moreover, as a means of centering the pickup 20, 21, and 23. To center this part 11 relative to the core 7, the cylinder bore 22 has a widening or counterbore 24 into which a sleeve 25 is entered. The sleeve 25 is integral with the surface of the base plate 13 in opposing relation to the flat surface of the core 7. The part 12 is, for example, fabricated of a plastic material and is provided with a flange 26 of a magnetic material adapted to be attracted by the magnetic field 6, 7. Thus, to move the carriage 1 in the direction of the arrow F one has to overcome the resistance of the magnetic force between the magnetic 6, 7 and the flange 26. In this way, assurance is provided that the carriage 1 cannot move spontaneously in the direction of the arrow F In the interior of one of the parts 11 or 12 an elastic stop 27 for the other part might possibly be placed. Though it is not illustrated in the drawings, it should be quite apparent that the parts 11 and 12 of the dash-pot may include other encased tubular protrusions, coaxial with the protrusions 15, 16, 18, and 19 to function as baffle plates for the air compressed between these parts. These other encased protrusions may slide in relation to each other by gentle friction so as to form pistoncylinder couples, or simply may slide with loose fitting engagement.

What is claimed is:

1. In combination with a positioning device for the displacement of magnetic heads of a magnetic tape device, a damping device, said positioning device comprising a carriage for magnetic heads mounted for sliding movement, an electric motor drivingly connected to said carriage, said electric motor including a permanent magnet having a cylindric magnetic core and a coil carried by said carriage for movement therewith and arranged in telescopic coaxial relation with said core, and said damping device being an air dash-pot positioned axially between said core and said carriage, said dash-pot including two component parts one each fixedly secured to said core and said carriage.

2. A device according to claim 1, characterized by the dimension of each of the two component parts of the dash-pot in the direction of the displacement of the carriage being relatively short in proportion to the movement of the carriage and said dash-pot component parts being free of interacting with each other except when the carriage is in the vicinity of said core.

3. A device according to claim 1, characterized by at least one of the component parts of the dash-pot comprising at least one cylindric protrusion projecting from a base plate and interacting with a cylindric protrusion of the other component part to form at least one cylinder-piston couple.

4. A device according to claim 3, characterized by the component parts of the dash-pot including each several other cylindric protrusions integral with respective base plates and coaxial with the first mentioned cylindric protrusions, at least one cooperating pair of said protrusions fitting with play.

5. A device according to claim 1, characterized by the two component parts of the dash-pot being arranged coaxially with the magnetic core and the carriage.

6. A device according to claim 5, including said carriage having a velocity pick-up positioned in a cylinder bore coaxial with said magnetic core, the two component parts of the dash-pot include base plates having tubular central protrusions projecting therefrom in co- 8. Device according to claim 7, characterized by said component part carried by said core being centered in relation to the core by means of a sleeve carried by the base plate thereof fitting in an enlarged cylinder bore of short length and coaxial with the cylinder bore containing the pick-up and the end thereof opposing said carriage.

9. Device according to claim 1, characterized by the component part of the dash-pot carried by the carriage including at least one magnetic section attracted to said core by the magnetic field thereof for preventing accidental movement of the carriage away from said core.

10. A device according to claim 9 wherein that one component part carried by said carriage has a cylindric protrusion extending outwardly from said carriage toward said magnet and the other component part has a cylindric protrusion extending outwardly from said magnet toward said carriage, one of said cylindrical protrusions being of a slightly greater diameter than the other of said cylindrical protrusions and each cylindric protrusion being arranged coaxially with the other to interact as a piston-cylinder arrangement when in engagement one with the other.

II. A device according to claim 9 wherein at least a portion of said one component part is fabricated of magnetic material disposed to be attracted to said core by the magnetic field for preventing accidental movement of said carriage away from said core.

12. A device according to claim 1 wherein said clamping device is disposed within said coil.

13. A device according to claim 1 wherein there are stop means associated with said carriage remote from said motor for limiting movement of said carriage away from said motor. 

1. In combination with a positioning device for the displacement of magnetic heads of a magnetic tape device, a damping device, said positioning device comprising a carriage for magnetic heads mounted for sliding movement, an electric motor drivingly connected to said carriage, said electric motor including a permanent magnet having a cylindric magnetic core and a coil carried by said carriage for movement therewith and arranged in telescopic coaxial relation with said core, and said damping device being an air dash-pot positioned axially between said core and said carriage, said dash-pot including two component parts one each fixedly secured to said core and said carriage.
 2. A device according to claim 1, characterized by the dimension of each of the two component parts of the dash-pot in the direction of the displacement of the carriage being relatively short in proportion to the movement of the carriage and said dash-pot component parts being free of interacting with each other except when the carriage is in the vicinity of said core.
 3. A device according to claim 1, characterized by at least one of the component parts of the dash-pot comprising at least one cylindric protrusion projecting from a base plate and interacting with a cylindric protrusion of the other component part to form at least one cylinder-piston couple.
 4. A device according to claim 3, characterized by the component parts of the dash-pot including each several other cylindric protrusions integral with respective base plates and coaxial with the first mentioned cylindric protrusions, at least one cooperating pair of said protrusions fitting with play.
 5. A device according to claim 1, characterized by the two component parts of the dash-pot being arranged coaxially with the magnetic core and the carriage.
 6. A device according to claim 5, including said carriage having a velocity pick-up positioned in a cylinder bore coaxial with said magnetic core, the two component parts of the dash-pot include base plates having tubular central protrusions projecting therefrom in cooperating relation and forming a piston-cylinder couple, and said velocity pick-up extending through tubular protrusions.
 7. Device according to claim 6, characterized by the component part attached to the core including a flat surface on the base plate thereof seating on a flat face or said core and the cylindric protrusion thereof having an inner diameter equal to that of said cylinder bore.
 8. Device according to claim 7, characterized by said component part carried by said core being centered in relation to the core by means of a sleeve carried by the base plate thereof fitting in an enlarged cylinder bore of short length and coaxial with the cylinder bore containing the pick-up and the end thereof opposing said carriage.
 9. Device according to claim 1, characterized by the component part of the dash-pot carried by the carriage including at least one magnetic section attracted to said core by the magnetic field thereof for preventing accidental movement of the carriage away from said core.
 10. A device according to claim 9 wherein that one component part carried by said carriage has a cylindric protrusion extending outwardly from said carriage toward said magnet and the other component part has a cylindric protrusion extending outwardly from said magnet toward said carriage, one of said cylindrical protrusions being of a slightly greater diameter than the other of said cylindrical protrusions and each cylindric protrusion being arranged coaxially With the other to interact as a piston-cylinder arrangement when in engagement one with the other.
 11. A device according to claim 9 wherein at least a portion of said one component part is fabricated of magnetic material disposed to be attracted to said core by the magnetic field for preventing accidental movement of said carriage away from said core.
 12. A device according to claim 1 wherein said damping device is disposed within said coil.
 13. A device according to claim 1 wherein there are stop means associated with said carriage remote from said motor for limiting movement of said carriage away from said motor. 